The cracked window of iFix, a store on the Upper East Side that repairs broken electronics. It was smashed on July 19 when four boys tried to steal display phones, which were fake.CreditRichard Perry/The New York Times

The sign on the Upper East Side street looks so realistic, people stop and lean closer.

“Broken Smartphone?” it reads. Beside the lettering is a blown-up version of an iPhone, several feet tall, with long, spider web cracks spreading across its screen.

Smaller letters on the sign read, “Warning!” but people ignore that and reach out to touch the screen.

The glass, it turns out, is real, and so are the jagged cracks. Evidence of a petty crime that, with some luck and quick thinking, became an unintentional display of guerrilla marketing.

The luck resided in the location of the sign. It is not a window to a barber shop or a dry cleaner or a bodega, where broken glass is broken glass, something to be replaced quickly. It is an iFix store, a shop that repairs broken electronics, mainly ones that begin with a lowercase “i.”

Viacheslav Sukhachev, an owner of iFix, arrived at work at the East 77th Street shop the morning of July 19 and saw the lower front window had been smashed. The window looks down to the basement, where the repairs are done. They use the window to display iPhones, but the phones are fake, just for show. Upstairs is a small waiting room with a PlayStation for customers.

Nearby is a security camera facing east. Mr. Sukhachev, 29, from Siberia, installed that camera and others after a burglary at his neighbor’s business, the Lifshitz Gallery, in March. The burglar broke through a rear wall and stole about 450 watches; some were expensive Rolex models that the gallery owner had repaired, a crime described in this column in May.

A couple of women who lived nearby entered the store that July morning and said they saw the window-smashing. At the same time, Mr. Sukhachev watched the feed from the camera on the sidewalk.

One of the women said, “‘It was kids who did it,’” Mr. Sukhachev said. “I’m thinking, kids in their 20s? But no.” He watched the video: “It’s literally kids.”

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After watching a security video, Jay Caraballo, a salesman at the store on East 77th Street, said the would-be burglars looked like boys who had visited in July.CreditRichard Perry/The New York Times

On the screen, with the time stamped near 4 a.m., four boys pass the store, walking east. Three are almost certainly teenagers, while the fourth, much shorter, looks to be closer to 10. Two of the teenagers are bare-chested on a hot summer night, each with a shirt draped over one shoulder. They are ambling along without any sign of purpose.

An hour later, at 5:01 a.m., they come back the way they came, but now one teen is on a bicycle, and another is puffing from appears to be a marijuana cigarette. As they approach the store on the video, the smallest boy reaches out for it and takes a long drag.

The camera was angled away from the display window, but it picked up the sounds of banging moments later. The would-be burglars did not know that the glass was shatterproof. After many strikes with decorative bricks that had been beside a sidewalk tree, they gave up and left. A window that looked breakable but was not had stopped them from stealing iPhones that looked real but were not.

Mr. Sukhachev called the police, and officers came and wrote a report. An officer looked at the window, and at the sign for the store standing on the sidewalk, showing a broken iPhone screen.

“It’s really ironic,” the officer said, according to Mr. Sukhachev. “Look at that sign, and look at the window.”

Mr. Sukhachev called a sign maker in New Jersey and described what he wanted in a new sign, including the indicator of signal strength in the upper left corner and battery life in the upper right.

A salesman at the store, Jay Caraballo, watched the video later. The boys looked familiar. He rewound several days of video from a camera in the waiting room, and there they were, on July 10, playing with the PlayStation. They look like the same boys.

“I talk to everybody who comes through my door,” Mr. Caraballo said. He said the boys told him they were from uptown, but came to the neighborhood for the public pool nearby.

They haven’t been seen since.

The plan was to replace the window, but that quickly became expensive and complicated by the fact that its frame is embedded in the wall. And the new look is getting a lot of attention. Mr. Sukhachev said they might just cover it with film to prevent anyone from cutting themselves on the glass and leave it at that.

A version of this article appears in print on , on Page A14 of the New York edition with the headline: Phone Repair Shop Turns Thieves’ Failure Into an Eye-Catching Advertisement . Order Reprints | Today’s Paper | Subscribe